text:
Is it possible for a non-towered airport to have keyhole extensions Class E starting at the surface?
(skyvector.com, modified)
The Springfield, OH airport, KSGH, is a non-towered airport with both precision and non-precision instrument approach procedures. To support these approaches, there are a couple of "keyhole" Class E transition areas; however, these particular Class E transition areas start from the surface (magenta dashed lines) depicted on VFR Sectional Charts.
I'm really confused how the Class E areas extend from the surface when the airspace directly over the non-towered airport is Class G. Is it possible that the VFR Charts are in error and the magenta dashed line should be removed or converted to a magenta vignette indicating that the Class E starts at 700' AGL?
There are several indications in my mind that this is simply depicted as an error on the VFR Sectionals:

The VFR Sectional says, "See NOTAMs/Supplement for Class E (sf) eff hrs"; however, when consulting the Central Eastern Supplement for KSGH, there is no "Airspace" item listed under the airport.  Which substantiates the VFR Sectional chart designation that the airspace directly above the airport is Class G.
Since there is no "Airspace" in the Supplement (nor NOTAMs), there is no "effective hours" as the VFR Chart suggests that there should be for the two depicted Class E (sfc) areas.
As depicted, it appears as if the a pilot could enter Class E controlled airspace and then quickly transition out of it and into Class G uncontrolled airspace as they continue on the approach.  This doesn't make sense when you consider the intent of the Class E transition areas are to help IFR traffic be provided separation from Class G traffic.
The Airman's Information Manual (para 3-2-6.e.2) describes "Class E airspace may be designated as extensions to Class B, Class C, Class D, and Class E surface areas."  It does not include Class G airspace in that list of airspaces that Class E may be designated as an extension.
The AIM (para 3-2-6.e.2) goes on to say, "Surface area arrival extensions become part of the surface area and are in effect during the
same times as the surface area." Since there is no surface area in effect, it seems to be another indicator that the Class E (sfc) is also not in effect.

Can anyone explain how it's possible for these two Class E (sfc) areas to be legitimately marked, or are they simply errors?

Airspace directly above KSGH is Class E at 700' AGL.  There is the magenta vignette surrounding a big area on the sectional chart.

My guess is that there was Class E or D to the surface surrounding the airport in the past, which was subsequently eliminated, but the extensions were not changed.

There was a control tower at SGH which closed. The FAA issued a rule which removed the Class D airspace as of December 10, 2015.
This leaves the class E airspace chunks. As you noted, the Chart Supplement for SGH has no information about the airspace, and FAA Order 7400.11A (the current version of airspace definitions) states only that, after an initial NOTAM announcing the effective dates and times, (p. E-183)

The effective dates and times will thereafter be continuously published in the Airport/Facility Directory.

So, is the airspace between the surface and 700AGL in these two areas class E or G? I'm not a lawyer, but I think you could make a strong argument for the airspace being class G, unless the chart supplement gets an update or a NOTAM is issued.
Finally, to the question: why are these two areas there? Two thoughts come to mind.

The class E extensions existed alongside the class D airspace, and nobody thought to remove them. (This is the most likely, to me.)
There is some other operational reason for the class E airspace. There are instrument approaches to the field, though they terminate well inside the radius of the two airspace segments, so that's not very likely. Also, the class D airspace could be reactivated by NOTAM if a high-traffic event at SGH were to occur; the class E extensions could be part of that. However, both of these options are really stretches - my guess is that we've found airspace that someone just forgot.

2019 update: those extensions are no longer visible on the sectionals:

(skyvector.com)

Yup, this is what I thought too. Thanks for confirming what I was seeing.  Why is it important? I am also a Remote Pilot (Part 107) and if this airspace is Class E to the surface, we are restricted from flying within the lateral boundaries without an FAA waiver, even if though we are restricted to flying below 400'.  And the FAA is very slow at approving these waivers.  However, filing a waiver request might give them a little more reason to fix their oversight.  The other funny thing about this is that KSGH is in the process of getting special permission to fly UAVs at the airport!

Here's are links to information about civilian and military organizations attempting to get approval to operate UAVs out of this airport.

BTW -- aircraft on the IAPs are well above the 700' AGL floor of the surrounding E airspace when in those "keyhole" areas, so that's not why they were left behind.

Everything in the above answer is true; the last guess at the end is the correct one. I found an authoritative link that enables a shorter answer.  Re the Remote Pilot's comment --see the January 10 2018 Memorandum re SUA flight in class-E-to-surface extensions-- http://goldsealgroundschool.com/uav-library/surface-E-authorizations.pdf-- as discussed here https://aviation.stackexchange.com/questions/35297/which-parts-of-class-e-airspace-can-an-ultralight-part-103-fly-in-without-prio/55714#55714 .  You should be fine to fly in those keyholes. A bit late to tell you now--

The above comment should have read, "the first guess at the end is the correct one."

@scottfred  -Re the note from a UAV (part 107) pilot several comments up-- you should have been to fly in those areas anyway even when they were E4.  See for example related question https://aviation.stackexchange.com/questions/63970/what-is-the-primary-reason-that-the-non-towered-airports-kacv-and-ktlv-have-e4-e especially the content in item 5.  However the Jan 2018 Gardner memo dates from well after your Feb 2017 comment, and you are no doubt very familiar with it by now.

Class-E-to-surface "extensions" are supposed to abut Class D or higher airspace, not stand alone like this.  Or they can abut a Class-E-to-surface circle or other shape surrounding the airport in question-- most frequently this involves the particular case where Class D or higher airspace surrounding the airport has temporarily reverted to Class-E-to-surface due to the tower being closed for the night.  There are however a few exceptions where no tower is involved, and full-time Class-E-to-surface "extensions" abut a full-time Class-E-to-surface circle around the airport-- some examples are given in the related ASE question What is the primary reason that the non-towered airports KACV and KTVL have E4 extensions to E2 airspace? .  So the literal answer to the actual title of your question is "yes".  However, Class-E-to-surface "extensions" are never supposed to stand alone as illustrated here.
The FAA simply forgot to remove the Class-E-to-surface "extensions" after they closed the tower and removed the Class D airspace.  They are fixing it now-- the "extensions" will go away in November 2018.  See-- https://www.federalregister.gov/documents/2018/09/10/2018-19475/revocation-of-class-e-airspace-springfield-oh

Kind of late to run across this question now but better late than never?

Have since learned that it's possible for an E4 extension to adjoin an E2 circle even if no tower is involved-- see for example https://aviation.stackexchange.com/questions/63970/what-is-the-primary-reason-that-the-non-towered-airports-kacv-and-ktlv-have-e4-e . This is extremely rare though, and could not account for E4 extensions simply standing alone not connected to anything

(ran across this old answer again recently and edited to include info in last comment)


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Is ADS-B intended to replace other traffic management systems?
What is the main purpose of ADS-B? How do aircrafts interact with each other using them?
Is it intended to replace the Traffic Collision Avoidance System (TCAS) or ground based Air Traffic Control (ATC)?
Also, why they need the Global Navigation Satellite System (GNSS)? Are there other systems that has a dependency relationship with ADS-B?

http://www.flightradar24.com/how-it-works can be a good starting point.

There is too much included here. This should be separated into multiple questions.

For a short introduction on what ADS-B is and why it is called dependent see this answer.
ADS-B is a surveillance technology whereby the aircraft broadcasts information about its identity, position, altitude and velocity of the aircraft to any interesting party. The position and velocity information is derived from GNSS (GPS).
TCAS
ADS-B is not intended to replace TCAS, although in the future it will augment TCAS. The TCAS algorithm currently only uses distance and altitude to calculate whether there is a conflict and to determine the best conflict resolution strategy. With the more accurate ADS-B position available to the system as well, the number of TCAS interrogation can be reduced (the surveillance radio frequencies are getting congested in some areas) and the performance of TCAS can be improved. A new standard for this hybrid approach was published in 2013.
It may also be possible to have a passive TCAS-like system that does not require active interrogation but is purely depending on ADS-B. Currently a technical standard for a new Airborne Collision Avoidance System (ACAS, the generic name for TCAS) is being developed in a joint RTCA / EUROCAE committee (RTCA SC-147 / EUROCAE WG-75), which will take advantage of more data offered by ADS-B. This new standard will eventually replace TCAS II.
A 'TCAS light' for small aviation has also been developed based on ADS-B. It is called  Traffic Situation Awareness with Alerts (TSAA), a standard that was published last year. Within the next couple of years we will see manufacturers start offering products based on this standard.
ATC
The purpose of ADS-B is neither to replace ground based ATC. But it will change the way ATC is done. ADS-B IN will improve the situation awareness of pilots; they will have a display of accurate positions of other aircraft. New procedures will allow pilots to maintain visual separation to other aircraft in marginal Visual Meteorological Conditions (VMC), where they currently would often lose sight of other traffic. A more advanced usage of ADS-B will be flight deck based interval management (FIM) where ATC will be able to instruct aircraft to 'follow that plane XX seconds behind for landing on runway YY'. A first technical standard for FIM is being worked on, it is intended to be published before the end of this year.
ADS-B is neither a replacement for all radars, although it will allow the number of radars to be reduced. For remote areas that currently do not have radar coverage because of the associated high costs, ADS-B will be a cost effective alternative. Over the oceans, satellite ADS-B receivers will be able to provide surveillance, changing the way ATC is performed over the high seas.
GNSS
Given the examples above, it is easy to understand the requirements on the reliability of ADS-B are substantial. Not only must the system be able to deliver accurate position data, it must be able to deliver that data with high integrity. That means, the probability that the system transmits inaccurate position data, even when there is a failure in the system, must be extremely small. To achieve this, a positioning systems must be able to do internal cross checks to detect failures and not depend on possible erroneous inputs from humans. GPS can meet the position source requirements using Receiver Autonomous Integrity Monitoring (RAIM).
The ADS-B technical specifications have all been written in such a way that they do not explicitly require GNSS to be the position source, but at the moment it is the only system that meets the requirement effectively. Most certification documents are written with the assumption that a GNSS will be used to provide position data. Theoretically one could put another system forward, but the costs of certifying that would be very high.

Is GNSS the generic name for GPS, GLONAS, et cetera?

@raptortech97 Indeed. GNSS = global navigation satellite system

ADS-B will eventually replace transponder+secondary radar as the primary means of separation.
Transponders+secondary radar will be kept for a long time as a backup.
Right now the authorities are saying it won't replace it, because they don't want the pressure to stop having to keep transponders in the long run.
ADS-B is a much more sophisticated way to do aircraft separation.
In order to know how far another aircraft is from you, you need to interrogate it. Send out a pulse and time the response. Measure the general direction the response came from. The response contains the altitude of the contact. This allows ATC and TCAS to know where the traffic is (position and altitude). ATC radar compares this information over time to estimate course and speed.
ADS-B sends all this information automatically every second. GPS coordinates, altitude, forward speed, vertical speed, course, heading, and desired course/altitude (when its changing).
This is leaps and bounds better than transponder+tcas/secondary radar.
Also its new technology. We need at least a decade fully operating it worldwide before we can talk about retiring secondary radar and transponders.
In my view its not a matter of IF, but WHEN its going to happen.
My credentials ? I'm an IFR rated private pilot, a computer technology professional, and a telecommunications specialist with just enough experience in every piece of the operational/technology puzzle that makes the whole thing work.
The key fact is that airliners transmit ADS-B over the same frequency as transponder responses flow through. Eventually transponder responses will overwhelm the bandwidth needed for ADS-B traffic, making ADS-B unsafe. At this point ATC will be forced to create large transponder off zones. That will be the beginning of the end of transponders.
With ADS-B another aircraft in the area is just one extra message per second.
With transponder another aircraft in the area potentially adds another X messages per second where X = number of interrogators asking for a transponder response (including ATC and TCAS systems).

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What exactly is VMO and how does it affect a plane when it is exceeded?
I read an article that mentioned "VMO" speeds of a 747 and that the plane, when it exceeds its VMO, shakes uncontrollably and destroys itself.
I've never heard of planes doing this and the article explained VMO in a way that is beyond my understanding.
For someone that doesn't know much about aviation:
What does VMO stand for and how does it affect planes when exceeded? If it does cause the plane to shake to the point that it destroys itself, why is that?

related: http://aviation.stackexchange.com/questions/3373 http://aviation.stackexchange.com/questions/3088

$V_{MO}$ is a “maximum operating speed”. It is one of many “V-speeds” defined for an aircraft that limit operation at various flight phases. All V-speeds are indicated airspeeds¹.
The $V_{MO}$ is the maximum permitted speed for the aircraft. This includes a safety margin, so pilots can reasonably fly near that speed. Exceeding it is not immediately dangerous, but as it reduces safety margins, is an incident that should be investigated.
There is another speed, $V_{NE}$, the “never exceed speed”, which is somewhat higher and which marks the point where things start to get dangerous. When the aircraft exceeds $V_{NE}$, aeroelastic flutter may develop that will destroy the aircraft and/or important parts may break off as the dynamic pressure becomes higher than what they are designed for.
Also these speeds have their Mach number counterparts², $M_{MO}$ and $M_{NE}$. At high altitude, the same indicated airspeed (IAS) corresponds to much higher true air-speed, since indicated airspeed decreases with pressure, while the same Mach number corresponds to slightly lower true air-speed, since speed of sound only depends on temperature. So at high altitudes, the Mach limits are reached first while at low altitudes the IAS limits are.
Exceeding the $M_{NE}$ has different effect, though also dangerous. Above that speed flow separation occurs above the wing due to supersonic speed of the flow. This leads to loss of lift and significant down-pitching moment (a.k.a mach tuck), which aircraft not designed for supersonic flight may not have enough elevator authority to compensate.

¹ The airspeeds are given as IAS, the speed measured by pitot probes, so they can be directly compared to the indication in cockpit (aircraft with EFIS (“glass cockpit”) usually correct those measurement errors that can be estimated, showing so called calibrated airspeed (CAS)). However it may not be just a simple number but may be tabulated depending on other parameters.
In particular $V_{NE}$ and $V_{MO}$ may depend on altitude, because flutter depends on true airspeed (TAS) and at lower density (due to lower pressure at altitude) the same TAS corresponds to lower EAS/CAS/IAS.
² Mach number is true airspeed as fraction of speed of sound. In this case the limiting factor is formation of shockwaves due to the flow speed locally exceeding speed of sound around some parts of the aircraft.

I was warned that VNE (Never Exceed) is actually a true air speed, not indicated. It reduces with altitude. A small distinction but maybe an important one. Apparently most of the others are indicated airspeeds as you say.  (It's just a little unclear that VNE can actually be variable.)

@Andy: Be carefull: that's calibrated (CAS) not true (TAS) air speed.

Thanks for the explanation, I'm content now. (My VNE case was for gliders by the way, which tend to suffer from particularly low limits. Doubt it matters as much for most types.)

@Andy: Hm, thinking about it again, I am not actually sure whether aeroelastic flutter and divergence depend on EAS or TAS. They may in fact depend on TAS, in which case $V_{NE}$ would indeed decrease with altitude (it would still be expressed as IAS, just not as single value, but as table depending on altitude; the other V-speeds also depend on parameters, though for most of them it is weight)

Im 99% sure it is depending on CAS. Well, EAS if you want to be pedantic, but the compression factor is very small (and constant) for the speed ranges we are talking about, so I suppose it makes more sense to display them as CAS in the manual. Let me find a source on the net about this...

Also, I'm just going to be obnoxious and say it, but having read the answer only now: Mixing Vmo and Vne makes no sense. Vne and Vno are part of one certification, while Vmo and Vdf part of another. An aeroplane will either have one or the other.

Vne varies with TRUE airspeed. This is especially critical for gliders which have a low Vne and which fly in wave at high altitude. Many glider POHs and placards have Vne tables for altitudes of 10,000ft and above.

@rbp: Well, the Vne, as IAS value, varies with pressure altitude, because there is a TAS limit. But yes, that confirms that flutter depends on TAS rather than EAS.

(actually, it varies with density altitude as dynamic pressure depends on density, not static pressure)

IAS corrected for pressure (and, less important, temperature)  altitude is called???

Well, a glider is not really a fair example, since they don't have a proper service ceiling, so all they can do is give you this Vne vs alt table. I'm willing to bet those Vne values for 10,000ft and above are IAS though.... Here is the only proper source I could find on the net about this ( nice read anyway) : https://www.scribd.com/doc/84074210/Print-VNE-Revisited-Aviation-Safety-Article

@Radu094, gliders are important example, because they are primarily limited by flutter due to their long wings. There are other limiting factors that depend on IAS and transsonic aircraft are limited by Mach number, so for different classes of aircraft the $V_{NE}$ dependency on altitude looks differently.

Well, that was my point aswell: that gliders are a special case. I guess (like in the article I linked) you could say that Vne is sometimes IAS and sometimes TAS (if flutter is limiting) ?

Vne is in True Airspeed. I have added an answer with the table from the ASK-21

Vne is defined in terms of True Airspeed (TAS), while all other V speeds are Indicated airspeed (IAS).
Gliders are particularly susceptible to the aerodynamic issues that define Vne because they fly at high altitudes and have long wings.
Since determining true airspeed in the cockpit would require a calculation, gliders have tables in their flight manuals and placards in the cockpit that show Vne in indicated airspeed at various altitudes.

The table (which is barely visible) lists values of $V_{NE}$ depending on altitude. These values are indicated speeds, intended to be directly compared with the altimeter reading. The actual limit is a true airspeed, but $V_{NE}$ is the listed value and that is still indicated speed. Also, the limit is a true airspeed if the aircraft is flutter-limited. There are other possible limits with different characteristics.

Yes that's what I wrote. If it's not clear make a suggestion

Ok I tried to make it clearer and added two more tables. Some of these POH PDFs are hard to read.

There have been several incidents where a Boeing 747-SP, B747-100, B747-200, and B747-400 have exceeded not only Vmo, Mmo, and the Vne speeds and still survived, not “shaking itself to pieces.” These aircraft were damaged, of course, but there hasn’t been a case of the B747 aircraft ever being lost due to a catastrophic in-flight breakup due to the excursion of exceeding the Vmo, Mmo, and/or Vne speed/Mach numbers.

This answer only addresses half of the question, and does not talk about the definition of Vmo.

I think we need to study more! To understand these speed, we need to refer to Part 25 for transport category airplanes and Part 23 for Normal category airplanes. Such as Cessna, Piper or Diamond Et.al. Regs. such as 25.335 Et.al. and for Normal category 23.2160 of 23.2165 Et.al. Opinions without proper understand of Part 25 or 23 regarding each airplane category, are just that "Opinions" and lead to a misunderstanding of the subject.

would you like to address such points? or should we take your answer as being nothing more than a mini rant?

Hello John, welcome to aviation.stackexchange.com. The format of this site is Questions  & Answers. If you would address the questions with an answer that explains Vmo in the context of Part 23 and Part 25, that would be valuable. Your current post does not answer the question and will likely be removed by the community.

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Is a Mooney M20 a difficult plane to fly as a beginner?
I am considering purchasing a Mooney M20 for 60k to fly for my initial certification. I'm not sure if this seems like a logical choice on the surface but let me explain my reasoning. I travel quite a bit. I live in the Dallas area and drive to Houston, Austin and San Antonio regularly. I average 60 hrs in the car a month traveling. This aircraft would be used for travel on a regular basis, 15-20hrs a month. The speed of the mooney is what is most attractive to me. I considered a 172 but the faster Mooney will save me valuable travel time. I will occasionally have 2-3 passengers with me.
My questions are:

Am I crazy?
Is a Mooney a difficult aircraft to learn in?
Should I suck it up and pay the rental fees and buy the Mooney after I get my license?

Not specific to the Mooney, but you might want to read: In what cases does it make sense to buy a plane before you begin pilot training?

You won't know any better!  You'll learn how to fly a Mooney.  Not a big deal.  Yes, you can use it for PPL training.

You need to be a bit more specific as "M20" refers to a lot of aircraft. An older M20C or M20D (with the fixed gear) should be quite manageable. An M20TN Acclaim is out of the question. Since you mention 60K I assume you are talking C/E variant but clocked out J's can be had for that. You can likely find an A/B but wooden wings are not for new owners or the faint of heart.
I have a Private Pilots License, an Instrument Rating, and a Complex Endorsement (which you need to fly just about any Mooney aside from the fixed gear D model) and have been pretty seriously looking at buying a Mooney as well as flying a few. Here are some thoughts:
The older Mooney's are on par with the other various trainers (PA-28/C172) size and load wise but tend to be about 10-15% faster on 10% less fuel. When it comes to flying, speed is generally what makes an aircraft "harder" to fly. The faster you go the faster things happen and the more likely you are to make a mistake or enter some airspace you shouldn't. In a Mooney, which is generally a faster plane you are of course more likely to have these issues.

You need to consider when training in a complex aircraft you are adding two additional things (gear and prop control) to an already confusing environment which can add to training time and increase your chances of messing something up.
Buying an aircraft for training can save a lot of money in the long run but what if you end up not liking it?
Although rentals are not always super well equipped in my experience they tend to be pretty well maintained as the flight schools are in the business of making money, so you dont lose training to the fact that you cant afford some AD or other maintenance issue.
Insurance premiums on a complex aircraft may be high for a new pilot. I can tell you that premiums for an M20C/E once you have your license are reasonable.
Mooney's have their own maintenance quirks but with the recent PA-28 spar issues that pretty much every GA plane has some kind of pricy issue.
You may want to define 2-3 passengers a bit better, a significant other and two kids is a lot different than 3 other "buddies". The back of most light aircraft is not exactly the most comfortable place.

I would take a serious look at this guy's thread he has a D model he has been working on for some time. The tale is a good example of what you are in for.

When was an M20 ever made with fixed gear??  I think you mean the manual johnson bar gear no?

@JohnK The M20D did have a fixed gear variant they were called the "master model" produced from '63-'66. However a conversion to the retractable was available and many have been converted so there are not a whole bunch left flying around.

WOW.. Learned something new.  Thanks!

Don't buy an early M20 with a wooden tail structure- if you must look for an old one, make sure its tail has been converted to a metal structure. Furthermore, the rumor is that there is now only ONE A&P mechanic nationwide who is qualified to do annuals on mooneys with a wooden main spar and a plywood wing skin (i.e., the M20A).

Not sure about the US, but I'm pretty sure you aren't allow to fly an RG aircraft or an aircraft with a variable pitch prop without a complex endorsement, which means you won't be allowed to solo in your Mooney during your initial training...

@jwenting In the US you can receive a complex endorsement during initial training and solo in a complex aircraft if you chose. Nothing in 61.31 stipulates you have to have a license. Some discussion on it here and here

Yes learn to fly first at a normal school in their trainers and then go buy a Mooney and get properly checked out on it.  You go buy a complex airplane, which, lets not kid ourselves, regardless of brand is one of the best money pits there is (more than boats), and say you find you're not cut out for this flying gig after 20 hours of training.
Now you're stuck with a $60000 cow chewing up money late at night in the pasture (an old aviation metaphor)... crunch crunch crunch... watch those dollars flow... and you can't even demo it yourself to unload it; you have to hire someone to do that.
Some people have done it and succeeded, but the risks are high.  If you have no problem with dropping 60k and ending up another 20k poorer after the experience, go for it, but understand the risks.

I agree with the other answers, I would add on that you want to learn to fly in an airplane your instructor is familiar with, not just yourself. Mooneys are rare beasts, most instructors will never have been inside one. You want your instructor to know every knob, switch and lever in your airplane, you want them to know how to recognize and recover from all the bone-headed things you will do as a student pilot, like incipient stall recovery, spin recovery, etc. Instructors have hundreds or thousands of hours in the primary trainers they fly, it's safer to learn to fly in one of those.
Once you have some experience you can judge what airplane is right for you. Keep in mind a fast, complex single only really makes sense once you have an instrument rating in most cases, so you might want to get at least close to that before buying one.
Lastly, do you know a local maintenance organization or A&P mechanic who knows Mooneys? Mooneys have their quirks, you want someone who can fix them who isn't hundreds of miles away.

Thanks for all the comments! The Mooney I'm looking at is a M20F and its closer to 70k. There is actually a Mooney service center at the airport where I would be keeping the aircraft, Maxwell Aviation. I plan to pay Don Maxwell a visit to discuss maintenance costs. I will update the thread after I do.

Learn to fly first @Dewayne, that's my recommendation.  Figure out if you like it!

To answer the question is a Mooney M20 difficult to fly, the answer is no, it is not.  They do demand a smooth roundout and touchdown due to the stiff suspension on the trailing link gear.  As other have pointed out, it’s a complex airplane and is going to be more expensive to maintain and insure for a neophyte pilot.
A major difficulty for a new pilot to cope with is the speeds and capabilities of the airplane.  Expect a early model M20 to be about 50% faster than a Cessna 172 and modern turbocharged variants like the M20M Bravo and M20T Acclaim are capable in excess of 200 KTAS and operations as high as FL250.  They have more systems to operate and handle and offer a considerably larger flight envelope than a typical trainer like a PA-28 does.  This greatly increases your capability for using the aircraft for travel but it can also be a rope long enough to hang yourself with if you’re not careful.
Low time pilots are typically deterred from Mooneys for these reasons.  Similar to a new motorcyclist transitioning onto a 1000cc sport bikes, a low time pilot can get into one of these complex, high performance birds but needs to be aware of the risks in their operation.  If you intend to do primary flight training in one of these airplanes, while it can be done, It will inevitably be more difficult and costly to do so both for getting the aircraft flight time, as well as the insurance demands for a new pilot. Insurance companies may will set a minimum hours of dual time required before they will even let you solo the airplane and may demand that you obtain an instrument rating before even being allowed to fly the airplane solo as a private pilot.
Here’s what I would do: find a decent flight school with a nice 152 or 172 and do your primary flight training and that to get your PPL. Next obtain an instrument rating on your private pilot certificate, and then finally look into buying a Mooney or similar high-performance bird. If you do select a Mooney or Cirrus, or similar aircraft, seek professional instruction from the factory and schedule recurrent training with a factory instructor pilot.
In the time that it takes you to complete your private pilot certificate and instrument rating, I would also be researching Mooneys for a year or so and befriend a qualified mechanics who has experience in the M20 airframe.  You will need to employ him to obtain a pre-by inspection on one of these aircraft and it’s very useful to do so to avoid ending up with an airplane that has a lot of maintenance issues. It will also help you learn about the Mooney airframe and some of the things that can go wrong with it.

Thanks for your comment! I recently completed my FAA Medical exam and the medical examiner was also a flight instructor. The training aircraft he uses is an Alarus which I don't know anything about. Anyway, his rates are reasonable enough where I would not feel like I was throwing money away renting his aircraft for the lessons. Just a side note, I haven't been this excited about something in a long time!

Yes I fly CH2000s at my flight school.  It’s a solid and capable, if somewhat quirky, low wing, two place trainer.  It should serve you well for your PPL work.  In the meantime start learning more about Mooneys.

An M20F is a fine plane.  You can learn to fly it and use it for your PPL, no problem.
The engine is bulletproof, it's easy to fly, and it'll serve you well for years to come.  I have time in an M20F (converted to a 201) and completed my initial CFI in one.
Personally, I'd recommend abusing a flight school plane for your training but there is nothing wrong with using your own Bonanza, Mooney, Arrow, Meyers, or whatever as your trainer.  Many, many owners do this.  You MIGHT spend a few more hours on training but it won't be crazy.  Plus, you'll need the hours anyway to meet insurance requirements so you are going to pay for training in your M20F one way or the other.  Either during your PPL training or with an instructor after your PPL for some number of hours...25 to 50 I'd guess.
The only showstopper I see is getting insurance to solo.  Doable, but likely expensive.  You don't need insurance anyway so maybe you just accept 10hrs of risk for your solo flying.
Get the plane.  Fly it.  Enjoy it.  You'll be happy with it.
Be sure to do SB-208-B during the prebuy.

https://mooneyspace.com/topic/20137-sb-208b/  and  http://www.mooneypilots.com/mapalog/prepurchasehowwhy.html

Yeah...do a GOOD prebuy!

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How to interpret the Message amplitude in ASTERIX CAT 021 out of an ADS-B receiver?
As we know that the ADS-B use only in the reception so it's has own dynamic range.
The ADS-B ground station receives a signal from an aircraft and after the processing its will convert it to ASTERIX CAT021 formatted message.
When I checked the recording I noticed that the items I021/132 has the Amplitude message, in dBm, of ADS-B messages received by the ground station, coded in two’s complement.
And it's showing after deciding: -27 dBm
But when I convert it directly from Hex to Dec I found 0xE5 = 229.
What is the meaning here?

Could you be more specific with your question, than "what is the meaning here"?

IMHO, less on topic (or interesting) than the hijacker profile question.  VTC for lack of clarity per other comment, and no practical application to aviation.

Edit to tie this to a required maintenance function and I’d vote to reopen, otherwise it’s way too esoteric.  (Although you have a good answer now, so incentive is zero…)

ASTERIX Category 021, Item 132 Amplitude is a one-octet (eight-bit) fixed-length data item encoded in two's complement.
The octet 0xE5 (11100101) has the value $229_{10}$ if it is interpreted as a simple unsigned integer, but in two's complement it is interpreted as the decimal value $229-2^8 = 229-256 = -27\text{ dBm}$.


text:
What is the relation between ADS-B MOPS & quality indicators?
I have some questions about ADS-B & MOPS,

What is MOPS,
What is the relationship between MOPS and ADS-B out and Ground Station
Does the ADS-B have MOPS
If we have Ground Station with different MOPS at least than the ADS-B transponder, what will happen?
What is the relationship between MOPS and Quality indicators

A little feedback from the close voters would be nice…

@MichaelHall Close votes are about the post being too broad. and given that currently contains 5 questions, I see the point.

The MOPS stands for Minimum Operational Performance Standard. It is a document that describes exactly how the transponder should create and transmit ADS-B messages. The document is maintained by combined standardisation committees of RTCA (Standardisation Committee 186) and EUROCAE (Working Group 51). The document is named RTCA DO-260 (A,B,C,..) or EUROCAE ED102 (A,B,...)
The ADS-B MOPS (for 1090MHZ Extended Squitter)  went through various versions (DO260/ED102, DO-260A, DO260B/ED102A, DO-260C/ED102B .  The MOPS version used in the transponder is transmitted as a number in one of the ADS-B messages.

= DO260  / ED102
= DO260A
= DO260B / ED102A
= DO260C

Quality indicators
NUCp NUCv
NIC NACp NACv SIL SDA GVA NICbaro
More to be added later


text:
What are Market Share, Market Size & yield in aviation network planning?
I came across the terms Market share, size & yield in aviation network planning. I don't really know what that means, anyone can provide me with a simplified explanation or maybe a reference where I can read about it ?

These are terms not specific to aviation; they apply to business in general.

This might fit on [economics.se]. There doesn't seem to be a general [business.se], though this would probably be a perfect fit there.

These are terms not specific to aviation; they apply to business in general. But in an aviation network planning context they roughly translate to the following:

market size: how big is the market: i.e. what is the total number of passengers / tonnes of cargo travelling on a (set of) route(s)? What is the total sum of money spent on the route(s).
market share: what percentage of transport (in passenger number/tonnes of cargo, or ticket price) is provided by my company.
market yield: how much money does the ticket sales on this route bring?

Please, if a question is not on topic here do not answer it. It gives new users the impression that a question is accepted here.

Dear @Jamiec, thank you for leaving a comment. I am not sure whether this question is not on topic here. The terms are not specific to aviation, but within the context of aviation and network planning, they do have a specific meaning. I also note that nobody voted to close, but you decided use the moderator powers to close the question on your own.  In this case, I think that is unjustified and it basically prevents any consensus building in the community on which questions are acceptable or not. I respectfully appeal to the moderators to use their powers moderately.

Its comments like that which make me want to just quit moderating this community. Take a look at on-topic does this fall anywhere even close to those? I cant see how the answer would be anything but "no". YOU should have been the one to cast the first close vote! Not answer it.

I agree the question is both general, and applicable to aviation. As such, it seems about as proportionally on topic as some of the “how do I solve this equation” questions that stand here even though they might be a better fit on mathematics.

@Jamiec I thought the question was close enough to aviation to grace it with an answer. This site has historically many questions, some very well received, that are not strictly within the scope of our on-topic list. The list serves as a guideline...

...not as a hard rule. I think the community should be allowed to decide in these corner cases, form an "communis opinio". I am not trying to demotivate you as a moderator, quite the contrary. But I do invite you, and all of the community, to critically look at the way we moderate this site. In my opinion, the community moderation tools are sufficient for cases like this, and do invite the community to actively participate in the moderation and discussion on the health of this site

Perhaps StackExchange should allow moderators to optionally vote as regular community members, because the power of the diamond in the current form kills all opportunity to consensus building.

Despite this terms being somewhat used also in aviation, I don't see how this information is pertinent to our SE


text:
How can I become a master at the radios?
Are there any resources for student pilots who wants to get better at the radios?
Currently, I am immersing myself by using liveatc.com but what I am looking for is perhaps scripts between pilot and ATC so that I can study them.

Once you realize that 90% of the comms are a vocabulary of, what, maybe 30-50 words, it takes a lot of the pressure off.

Practice your radio calls with someone on the ground. It's best to work with another pilot or instructor. But, you can even practice with a friend or significant other.
You might find a script like this helpful: https://www.aopa.org/-/media/files/aopa/home/pilot-resources/asi/sampleradiocalls.pdf
Best of luck in your aviation journey.
-Matt

I would look at services like vatsim which offer real controller/other pilot radio integration into some modern software simulators. You can practice taxi instructions, picking up flight following, tower comms for class B,C,D airports etc.
Live ATC as you have noted is a great option.
Fly right seat with certified pilots, ask to operate the radios. If you are learning to fly you are likely near the GA section of the airport, if you hang around and get to know people, make friends, and maybe wash a plane or two you can likely get some right seat time and some radio practice.
There are a lot of great, free, radio recordings on Youtube although many of them pertain to IFR clearance practice which can be helpful if and when you get to that stage.


text:
How to determine runways at unfamiliar airports?
I’m having a hard time determining where the runway is. Let’s say I am 3 NM west of an uncontrolled airport and the runway is 18/36. An the active runway is 18.
What’s the best way to determine where the runway is?
I use the heading but because it still feels unfamiliar.
But to make the runway, I should just turn to a northerly heading that’ll put me on the downwind for that runway make my base turn then runway?
Does anyone have an easier way to do this?
I know you can use ForeFlight but I’m trying not to use it to better my skills.

Adding to the first comment, it is unclear if you are asking about proper pattern entry procedures, or how to acquire the field visually amongst the ground clutter.  In my neck of the woods there are many tall trees, and spotting a small unfamiliar runway when approaching from the side can be a real challenge.  Please clarify the problem.

I can cannot see the runway vertically but horizontally yes.In this scenario No I don't have avionics. I only have my DG. I know about the entering the pattern at a 45 to the downwind. Im coming from the stand point of having no Knowledge or visual reference of the airport ever other than A chart supplement. The answer cleared it up for me. but sometimes I am just a little unsure about where the runway would be located. I have my DG thats pointed directly west and my runway should be roughly 90deg to the right of me.

Here's a rather simple trick, look on google maps/earth using a satelaite view and eyeball some ground features coming from the you'll be coming from for real. ie/ prior planning. It really helps!

First thing first- you should endeavor never to put yourself in this position. By the time you are 3 nautical miles from an airport, you should have long since briefed your traffic pattern entries to the most likely runways (or, ideally, to every possible runway).
If you are in this position, you are behind the airplane. The best thing to do is slow down (mentally, not necessarily your airspeed) and take things one at a time. Fly over the airport well above pattern altitude. Look for traffic in the pattern. Identify the runways and visualize where the various legs of the traffic pattern are. Check that there are no closed runways or vehicles on the runways or anything. Frankly, you should be doing this even if you are ahead of the airplane- there could be NORDO aircraft in the pattern or something obstructing the runway, and you won't know if you just enter the downwind directly.
Don't even think about entering the traffic pattern until you're a few steps ahead of the airplane!
For actually navigating the pattern, a good way is to bug your heading indicator to the runway heading. When you are on downwind on a no-wind day, the bug should be on the bottom of the heading indicator, and it should be 90 degrees to the left or right on crosswind or base. Another way to think about it is that your downwind course should be the same as the heading of the opposite runway- so if you are landing on 18 your heading should be about 360 on downwind.
Keep in mind that you will need to compensate for winds so once you are roughly aligned to a leg of the traffic pattern you should be using ground references to ensure you are flying parallel or perpendicular to the runway.
Joining the traffic pattern as you've described would put you on the right downwind for 18. Unless 18 is designated as right pattern, this is actually illegal per 14 CFR § 91.126(b)(1). The FAA recommended entry to the left downwind is to fly over the field well above pattern altitude until you are a few miles past it, and then make a descending right turn (or a descent followed bu a right turn) and maneuver to join the 45 for the left downwind to 18.

You need to know several things:

Where you are in relation to the airport
The runway orientation relative to you
The traffic pattern being used there.

This is one of those situations were preflight preparation really helps to understand what you’re about to do. Prior to taking off heading for the airport, you need to have considered what the airport layout looks like, and what it’s going to look like from your perspective as you approach it from a certain direction.  Thoroughly read the chart supplement entries for the airport.  ForeFlight also offers 3D tools so you can look at the airport and visualized what it will look like as you fly towards it.  It also can plot traffic patterns and courses for entry into them for ease of reference.  Another excellent reference source are satellite photos of the airport in the surrounding terrain.  An airport may have good, visual, references, nearby, e.g., a sawmill, a Walmart, etc. and you can use the airport’s relation to these references to locate the field.
Airports, especially small ones, are (strangely enough) one of the more difficult objects to spot from the air during VFR ops in both day and night.  This is especially true if you happen to be approaching the runway in a direction perpendicular to it, which is one reason I do not recommend than my students select airports as visual waypoints on VFR cross country flights.  You may have to study the train very carefully, despite the field, but don’t become fixated on that that you ignore other visual duties, such as flying the airplane and seeing and avoiding other traffic.
Once you have determined which runway will be used and have the field in sight, you need to orient yourself to it.  A good way to do this is to use your gyro compass or HSI.  Note where the runway numbers are on the compass face, then draw a line between them in your mind on the face of the compass or HSI.  That line is going to be the orientation of the runway you’ll use relative to you.  Next, note what the traffic pattern is for that runway and where that traffic pattern will be relative to that runway
This is just one of the trickier things about entering the pattern at an untowered airport.  I wish I had a hard and fast rule for this, but I’m still in the process of formulating one.  One tip is, if the downwind leg of the traffic pattern is on the opposite side of the runway that you will be using, you were going to use a teardrop entry into the 45° entry onto the downwind leg.  If the downwind leg is on the side of the runway closer to you, you will maneuver the aircraft outside of the traffic pattern such that you can enter on a 45° entry into the downwind leg.
In you example you are 3 nm west of the airfield (I presume headed east).  Since the runway out at the airport is 18/36 and other pilots are reporting they are using Rwy 18 (or the winds in the AWOS/ASOS reports favor using Rwy 18) you know you intend a 45° entry into the downwind.  If the airport is not yet in sight, we can expect the runway to be oriented roughly perpendicular to your direction of flight with the approach end of the runway off to your left.  Next the traffic pattern.  Unless specifically noted on the sectionals and chart supplements, this will be a left hand traffic pattern.  From your orientation, and following the standard VFR traffic pattern entry procedures, you will be entering the patter on thd side of the field opposite to you for a teardrop entry into the left downwind.  This means you will be overflying the field at TPA + 500 feet (direct downwind entries are possible but discouraged at busy uncontrolled airfields for risk of a MAC. Once you have crossed over the airfield and clear of the vicinity of a traffic pattern, start your descent to TPA. Upon reaching TPA, then start your teardrop turn to get onto the 45° entry into the downwind leg.  In this case, you’re going to start a right hand turn until you roll out into the 45° entry.  Since the downwind will be flown on a heading of roughly 360°, You will roll out on a heading of 315°, then turning right with the appropriate spacing to your downwind heading.
Simple, right?  This is one of the finer points of flying into a untowered airports, and it often takes quite a bit of practice to get it right, especially at unfamiliar locations.

You orient the destination airport relative to a more obvious local landmark on your map, like a town or village or lake. Find the landmark, then start searching for the airport based on its position relative to the landmark, using other guides like road geometry.
If the airport is unfamiliar, you should fly over it 500ft above pattern/circuit altitude to reconnoitre things, like checking the overall placement of things, the wind sock, the apparent runway condition, etc. Join the circuit/pattern from the overhead.
Very important when going into an unfamiliar airport, especially an unlicensed private one where there may be power lines in unexpected places, look for the poles, not the wires themselves (unless the wires have those orange marker balls).


text:
How many pilots are required in an Airbus A380?
Is it possible for one single person to fly, maneuver and land an Airbus A380 by him/herself?

Related questions about single pilot flying on regulations, feasibility, and history.

One of the reason there is at least 2 crew pilots is that if one become incapacited in flight, the other can bring the plane to a suitable airport (e.g. for medical assistance)

If you needed two pilots to fly the plane, there would be four on board :P

In general, it is perfectly possible for a single person to fly modern aircraft like A380. However, regulations require the presence of 2 pilots (PF and PNF). In other words, technically yes, legally no.
In long distance flights, the aircraft usually carries two sets of cockpit crew (4, each capable of flying the aircraft) as the flight hours may be more than the permitted flying hours.

FAA Advisory Circular 25.1523-1 deals with the minimum flight crew in transport category aircraft. According to Section 5 Certification Procedures, Subsection c, Testing (vi) Incapacitated Crew member,

Whenever the applicable operating rule requires a minimum flightcrew of at least two pilots, the certification program should include a demonstration
  of operations during the total incapacitation of a crewmember at any point in a given flight. It must be shown that the airplane can be operated safely and landed safely with the remaining crew at a planned or unplanned destination.

I could imagine there are regulations requiring an aircraft to be controllable by one person only (or carry at least three crew if not) - is this the case?

@sanchises Yes. FAA AC requires that aircraft having flight crew of two should be controllable by one at any stage.

Indeed it was standard practice to carry 3 crew members when an aircraft required a minimum of 2 to (reasonably) operate

Doesn't the A380 have a second officer/flight engineer? Thought it was a three-man crew

@TomMcW: Most flights run by an A380 require an augmented crew due to flight duty hours -- if you put one on say the Tokyo-Fukuoka or Seoul-Jeju route though, that'd have only 2 crew up front, as the flight time on those routes is quite short (around 90mins for the former)

@TomMcW No, I don't think any modern Western airliner has a flight engineer (though some older ones in cargo service may still have one and I'm not sure about the Russian ones.) A380 only has 3-man or 4-man crew when using an augmented crew for long-haul flights like what UFO mentioned. For flights < 8 hours, they'd normally just have 2 crew.

Of course it is perfectly legal to fly an A380 with one pilot. You need to observe a few details, however.
For an explanation let me first say something about certification. When you compress all legal barriers to flight into one fact, it comes down to

Harm actively involved persons (like pilots) in less than one case per 100,000 (10$^5$) flight hours,
Harm passively involved persons (like passengers) in less than one case per 10,000,000 (10$^7$) flight hours, and
Harm not involved persons (like people on the ground) in less than one case per 1,000,000,000 (10$^9$) flight hours.

Now you can see where this is heading: If you don't take passengers onboard and fly the A380 as your recreational jet, you can do this with a private pilot license and all by yourself. All you need is a medical, the license and a type rating on the aircraft. And the aircraft must be airworthy, of course.
If, however, you carry others with you, you need to be 100 times more safe. This is accomplished by taking a spare pilot with you. In general, the second pilot shares the burden of flying, navigating and communicating with the first, but the aircraft has been designed to be flown by one pilot. Otherwise the second pilot would increase the risk of something going wrong - with two pilots you have twice the risk of one falling ill during the flight. Certification makes sure that one pilot by himself can fly and land the aircraft in an emergency.
Older designs needed as many as five people to fly the aircraft (first pilot, co-pilot, flight engineer, navigator, radio operator), and in some not all controls could be reached from the pilot's seat. Steering those was more like sailing a ship: The pilot would command a thrust setting, and the flight engineer had to adjust the throttles (and mixture, cowl flaps, fuel valves ...). On the A380, however, all essential controls can be operated from either seat, and in total a crew of two is sufficient to comply with all regulations, including those for commercial operation.

I've heard of 3-person & 4-person flight decks but which were aircraft requiring all 5 of these positions you mentioned? Especially the radio operator. Just curious.

@curious_cat: The most modern one would be the Antonov An-70. Russian (and Ukrainian) designs never considered a shortage of manpower. The first ones were the Zeppelins, which had a Captain plus two people operating the controls, one for pitch and one for yaw. Plus one engine operator in each engine gondola. And a special radio operator, too.

Are there any records of an A380 or comparable aircraft being flown solo recreationally? Else, I find parts of this answer a bit silly :)

@sanchises: Read the question carefully. What is it about? Right, the possibility of flying an A380 solo. And that exists. What specifically would be silly about explaining how that works?

John Travolta flew an ex Quantas Boeing 707 as a private aircraft - so a commercial aircraft as a personal aircraft has been done

Would you need a new type certificate for flying an A380 by yourself to be legal? I thought almost all modern jets were certified only for multi-crew operation.

You cannot legally fly any aircraft while contravening the aircraft flight manual. The AFM for the 380 says "minimum crew: two"

@PeterKämpf Fair enough. I assumed  (and you know what happens when you assume) this question was asking about the case of an emergency, but indeed it doesn't say that.


text:
What are these things hanging off the trailing edge of the wing?
What are these things hanging off the trailing edge of the wing?
I've seen them in almost all of the aircraft I've flown in, and can't remember if they're exclusively Boeing or Airbus.

You saved me from asking the same question, thanks! :)

You didn't save me from asking the same question. Whoops! I tried searching for "static wing" but this question never showed up. Oh well!

Those are static wicks -- Basically these are little wires screwed to the airframe.
Their purpose is to discharge the static electricity that an aircraft picks up moving through the air - especially in clouds.
The static discharge tends to happen at "pointy" protrusions from the aircraft - if this happened through antennas it could cause radio and navigation interference, so to prevent that static wicks are installed, providing a low-resistance protrusion for the charge to dissipate through (and as an additional benefit, dissipating the charge helps ensure your aircraft doesn't attract lightning strikes).
Here's a couple of closer pictures:

They also show damage in a lightning strike, so I would assume they help with that too.

These are static wicks or static dischargers.  They dissipate static electrical buildup caused by the friction of air flowing over the surface of the aircraft.  The air friction tends to separate electrons from their atoms just as rubbing a balloon tends to do, causing an imbalance of electrical charge on a body.  The wicks work by providing a pointed surface where airflow separates from contact with the aircraft body.  The excess charge tends to flow into the air and is swept away from the aircraft.

At the speeds aircraft travel, and over the large distance between their wingtips - hundreds of volts potential difference are commonly produced.
Impossible to measure, though, as your multimeter experiences the same PD across it's leads, and shows a zero difference!

@DefenestrationDay, I'd be a bit surprised if it's not actually thousands of volts or more. You can't measure the potential difference between the air and the skin of the airplane with a meter, though. Air isn't conductive enough (without being ionized first, at least) for the ground lead to be a true ground. It's the same reason you can't just hold the ground lead in the air to measure a voltage on anything else. Also, if you did ground the ground lead and attempt to measure a static charge on something, it would discharge through the meter itself (though relatively slowly.)

Even the static charges that you accumulate on yourself on a cold, dry winter day that cause you to get shocked when you touch something grounded are often up into the thousands of volts. Almost any time you see a visible arc from a static charge, it's a kV or so. Since it's just static, though, once current starts flowing, the potential difference drops very quickly.

Yes, typically kilovolts are required before the corona will ignite on the carbon fiber tips of the "wicks." Corona is required to exist on the sharp tips before they can function. If the voltage on the aircraft drops well below kilovolts, they stop working.  Also, it's easily measured, but using an "Electrometer" type of voltmeter, where the meter impedance is upwards of 10^20 ohms, not the usual 10^7 ohms of typical DMMs.   For electrostatic measurements, 10 meg ohms acts like a good conductor, a near-short circuit.   Instead we use a "field mill"-based electrostatic voltmeter.

You don't even have to travel at high speeds: skydivers (~120mph terminal velocity) in relatively large formations -- say anything over 20-30 people-- can pick up enough static electricity across the formation that you can feel the shocks ripple through your body.  They don't hurt, but you can definitely tell that you're getting zapped.

@ljwobker: Lots of people would consider 120 mph a very high speed indeed.  :-P

It's called static dischargers since aircraft body or fuselage is made up of metal and carrying tonnes of fuel and electronic devices, we will have to remove the static electricity charge from the fuselage to the air in order to not ignite the fuel or disturb the electronic devices, and that's how it's done ! :)


text:
How many antennae are there on a typical small aircraft, and how are they connected to the avionics?
As far as i know there are a bunch of antennas on board of a small (EASA CS-23) plane:

GPS is for GPS navigation in MHz
VHFVOR is for NAV and Glideslope/Localizer
ADF is for ADF
DME is for DME
VHFCOM is for COM

Questions:

So there are three, two or one VHF antenna?
How is the VHF signal split?
If I have two NAV instruments (KN53 and GNS430)
how would the antennae would be cabled to them?

There is also a transponder antenna.

Also, glideslope frequencies are in the UHF band.

The VOR/Localizer/Glide Slope antenna is usually V-shaped and points backwards on the vertical stabilizer of the plane. On some aircraft, they point forward. They look like old-fashioned wire clothes hanger wire. Newer versions can be blade shaped.  sometimes they are boomerang shaped like the old car phone antennas of the 90s.) They usually have a splitter that allows two radios to use the same antenna. e.g. splitter
COM Antennas are usually a white rod or blade. You can’t split the signal for a COM radio using a rod antenna so one antenna is required for each radio. Not sure about blade antennas.
A GPS antenna is usually somewhat teardrop or ovoid shaped. Garmin GPS You can’t split the GPS signal, so one antenna per device is required. Some ADSB systems have an embedded WAAS chip and need their own GPS antenna.
GPS and COM antennas can be combined.
IFR capable airplanes also have a marker beacon antenna. These can be embedded in the fuselage or external.
A transponder is required in most airplanes and they have their own antenna. These are a small 2" or so stick with a ball on the end. They are mounted on the bottom of the fuselage.
Airplanes in the US at least are required to have an ELT. Old style ELTs and some of the newer ones have a piece of steel with a spring-like coil in them. Newer versions are more aerodynamic.
ADF antennas come in a wide variety of shapes. Some of the newer ones look like GPS antennas.
DME antennas usually look like a shark’s fin.
Composite aircraft often have the antenna embedded in the frame so it is not visible.
This Cessna video describes all of the antennas on a modern C182. I don’t have most of them on my airplanes and the ones I do have look a lot different.

Here are some images of different antennas. These are all from aluminum bodies planes. Composite planes often have the antenna embedded in the skin, except for GPS and I don’t have any images of them.
In general, VOR, ELT, and GPS antennas are on the top of the plane. Marker beacon, DME, and transponder antennas are on the bottom.
Here’s a picture of the most common arrangement. VOR antenna on the tail pointing backward. Two COM antennas. If you look closely at the bump on the right, that’s a GPS antenna. The long wire is an ADF antenna.

Here’s another aircraft with a common arrangement. In this one you can see the ELT antenna just behind the cover. ELTs are always on the top.

Here’s a good picture of an ELT antenna.

Beechcraft often have a boomerang antenna for Com/ Nav/ Loc/ GS antenna.

Another type of ADF and a good view of VOR and one COMM.

I don’t have a good picture of GPS antennas. The bump on the right is the antenna.

VOR blade antenna and an antenna on the stabilizer that I can’t identify.

I haven’t seen many VOR antennas like this one.

ELT antennas can be blade shaped as well. I have a newer 406 MHz ELT antenna with integral GPS antenna for capturing position every 15 seconds.  Typically mounted on top of the fuselage in front of the vertical stabilizer (or fin).
http://media.chiefaircraft.com/media/catalog/product/cache/1/image/265x/9df78eab33525d08d6e5fb8d27136e95/e/l/elt_114-042600.jpg
Marker beacon antenna, usually mounted on the belly of the plane. Looks similar to my ELT, but for different frequency reception (70 MHz vs GPS L1 frequency up in the 1200 something MHz range)
http://media.chiefaircraft.com/media/catalog/product/cache/1/image/265x/9df78eab33525d08d6e5fb8d27136e95/C/I/CI_118.jpg
And the little stubby transponder antenna, also usually mounted on the belly
http://media.chiefaircraft.com/media/catalog/product/cache/1/image/265x/9df78eab33525d08d6e5fb8d27136e95/A/S/AS_AV22.jpg
or a blade variation
http://media.chiefaircraft.com/media/catalog/product/cache/1/image/265x/9df78eab33525d08d6e5fb8d27136e95/r/a/rami-av-74sm.jpg
Total count on my airplane:
GPS - top of wing
ELT/GPS - top of fuselage
Com1 - top of wing
Com2 - belly
Marker Beacon - belly
Transponder - belly
VOR for VOR/Localizer/ILS - top of tail
Seems like there should be a glide slope antenna also for the ILS. VOR antenna used for that also?


text:
How to decide on which side of the runway the approach path indicator (VASI, PAPI) are placed?
This answer provides pictures and drawing of implementation of both PAPI and VASI. In all pictures I found, I cannot figure if there is a rule to put those lights on the right, on the left, or on both sides.
Is there some rules to decide if the path indicator lights should be placed on the right or on the left side of the runway?

Path/slope visual indicators are usually located on the left side of the runway (as seen when approaching), but may be on the right side when impractical. Good reasons for moving the aid on the right side:

Obstacle clearance, terrain, intersecting runways or taxiways.
Interference may occur on the left side, between PAPI lights and nearby lights. This is emphasized in FAA AC 150/5340-30G - Design and Installation Details for Airport Visual Aids: "Because PAPI system is dependent upon the pilot seeing a red and/or white signal from the light units, care should be taken to assure that no other lights are located close enough to the system to interfere with the signal presentation."

Installing them on both sides is beyond ICAO recommendations and FAA orders, but can be done:

For visibility improvement
In order to give better roll guidance

Some countries don't implement ICAO rules the same way, for instance in the UK, PAPI for governmental airports "may be provided on both sides of the runway" (source)
For airports providing a visual guidance for STOL operations. The PAPI associated with the steeper approach path may be located on the right side of the runway (source).

PAPI at the usual location, on the left side of the runway (source).
From Wikipedia:

The international standard for PAPI is published by the International
  Civil Aviation Organisation (ICAO) in Aerodromes, Annex 14 to the
  Convention on International Civil Aviation, Volume 1, Chapter 5.
  National regulations generally adopt the standards and recommended
  practices published by ICAO.

From FAA JO 6850.2B - Visual Guidance Lighting Systems:

The basic PAPI configuration is described in chapter 1, section 2,
  paragraph 16, and is shown in figure 5-1. All lamphousing assemblies
  (LHA's) should be located on the left side of the runway, as viewed
  from the approach direction. However, where terrain, cross runways,
  or taxiways make this arrangement impractical, the light units may
  be located on the right side of the runway.
[...]
The VISUAL APPROACH SLOPE INDICATOR (VASI) system is no longer
  installed by the FAA as a new facility. Specific details and installation
  criteria have been moved to Appendix E to provide technical support for
  existing VASI equipment and facilities.
[...]
The basic VASI configurations are described in appendix D, section
  1, paragraph 1 and shown in figures 1, 2, 4, and 5. All boxes (or
  light units) of the two-box; four-box, and six-box configurations are
  located on the left side of the runway (as viewed from the approach
  direction). However, where terrain or cross runways, etc., make this
  impractical, they may be located on the right side of the runway.

Washington Dulles Int'l Airport  offer several location variations, chosen for practical reasons. There is a PAPI on the left side for runway 1C and on the right side for 19C, but a reverse scheme is used for 1R/19L, and 1L/19R is just standard:

In general, the PAPI is located on the left side of the runway. However, depending upon the runway / taxiway configuration, the PAPI can be located on the right.
According to the Aerodrome Design and Operations based on ICAO Annex 14 to the Convention on International Civil Aviation, the international standard for PAPI (and other runway lighting systems),

The PAPI system shall consist of a wing bar of 4 sharp transition multi-lamp (or paired single lamp) units equally spaced. The system shall be located on the left side of the runway unless it is physically impracticable to do so.

Most of the regulatory bodies follow the ICAO recommendations. As for PAPI on both sides of the runway, maybe they are there for improved visibility/redundancy.


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Can an airliner be refueled while the APU is running?
Race cars can be refueled while the engine is running. I assume this is a dangerous task done by highly specialised technicians.
If ground support is not available, an airliner may keep the APU running to be able to provide power to restart the engines.
If ground support is not available and refuel is needed, can an airliner refuel while the APU is running (technically and legally)?
If the question is too broad, it can be narrowed to best sellers (B737 and A320 families).

Why do you think it couldn't be? Most cars,  including the one in your driveway can be safely refueled while they are running, even by Joe Sixpack. The fueling locations are a significant distance from the APU, and APU operation shouldn't be affected by refueling.

In Ontario anyway, a car's ignition must be off for Joe Sixpack to legally refuel it at a gas station...

Things may have changed since I retired in 1999, but in the 1990s 747s were routinely fueled with the APU running at both of the 747 carriers I flew for. In fact, you had to have electrical power of some sort to use the normal pressurized underwing fueling. Without electrical power, one would have to use the overwing fuel caps and gravity flow. In 10 years on the 747, I never saw that done.

There are cautionary signs at every gas station in America warning you to turn off the ignition while refueling your car. I don't know if it is law or just a recommendation. There are also signs about not using your cell phone while refueling. While that's proven to be just another myth about cell phones, the signs remain. I think the "highly specialized technicians" involved in pit-stops are so because they need to be able to quickly insert the fueling nozzle into a still moving vehicle in order to minimize stop time (in many, but not all race categories).

There needs to be power to the systems before fueling as it is needed to operate the pumps; so either ground support or APU; where APU being the most commonly used simply as its quicker to get up and going.

@FreeMan The situation is similar in almost all european gas stations. For cell phones, I read somewhere that for previous generations, receiving a phone call could increase dramatically and suddenly the phone's power cosumption, thus possibly burning fuel vapors. I don't know if this is a myth but i'm not sure I want to try by myself.

Wandering far OT, @ManuH, but considering the number of wireless electronics used in a racing pit, I'm comfortable with it. Plus numerous studies have shown that there's nothing a cell phone emits that will ignite fuel vapors unless the phone physically malfunctions and creates a spark. Again, though, we've gone far afield and it's time to stop...

@FreeMan It is reasonable to think that unlike race cars, cell phones are not certified to operate into fuel vapor, and thus it may not be certain it cannot create sparks. But I agree a cell phone igniting fuel vapor should be improbable (but it seems HF radio could do it)

Refueling an airliner with APU running is a perfectly normal procedure and it is done daily all around the world. The APU is located at the tail cone partially to reduce the risk of fire spreading to the fuel tanks, which are normally in the wings and center fuselage.
Some operators and authorities (not all) restrict starting and/or stopping the APU while fueling.

Not all aircraft have APU in the tail cone. In particular the three-engined jets (B727, DC-10/MD-11) have it somewhere around the wing box as they don't have much space left in their tail cones.


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What airframe designer/manufacturer is credited with the first retractable landing gear system?
A quick follow-up to Why do planes always land on rear wheels instead of the nose wheels?
What airframe designer/manufacturer is credited with the first retractable landing gear system? I ran past the article on retractable gear over in Wikipedia without really finding an answer

It looks like the first plane that actually flew and had at least a partially-retractable undercarriage was a German racing plane, the Wiencziers Renneindecker, from 1911:

You can see the undercarriage designed to collapse to the rear, using a hand crank in the cockpit to lift the gear. Not a great idea by today's standards as the gear would be prone to collapse on landing, but it apparently worked well enough at the time.
There are plans for retractable landing gear dating back to the late 1800s, before powered flight in such a craft was ever achieved, but they didn't become common on planes until just after WWI. Even then, for relatively slow planes (<200mph) it remains common even today to keep the gear fixed and wrap the wheels in a cowl, as for only a ~4% increase in drag over a full retractable setup, you save a lot of weight and mechanical complexity. Notable fixed-gear craft in military service through WWII include the German Ju87 Stuka and the Nakajima Ki-27 "Nate". Though most of the American wartime air fleet had retractable gear as of just after the start of WWII, practically every WWII air corps draftee trained on either a BT-11 or one of the biplane trainers like the PT-13/17/18. Today, plenty of civvie small craft have fixed gear, such as the Cessna 150, 172 and variants, Piper Cubs and Cherokees, some Beechcraft Musketeers, etc etc.

Nice one! Welcome to Aviation.SE KeithS!

It still remains common for slow planes to have fixed landing gear.

Very much so; my first flight was in a Cessna 150, which has a nonretractable tricycle config, and a large number of small civvie planes are similar.

Nice! Uh ... the source for the drawing - if you would be so kind?

@Everyone: Try this site and search for "Wiencziers". It doesn't matter if you don't understand German, because the OCR is so horrible that the text is mostly illegible anyways. I seems they didn't train the engine on the old font. Interesting detail: The fuselage was made from steel sheets.

Plenty of aircraft still feature rearward-retracting landing gear, fwiw!

Good point, but every time I hear of gear systems specifically designed for reliability and durability (always a good thing on a plane), "forward-retracting" is in the same paragraph. Not only will the gear strut naturally be pushed further back into the open position by the landing stresses, but in event of a hydraulic failure many such systems allow the pilot to simply release them and let gravity and the airstream open and lock them. Side-retracting gear is the next best especially with single-wheel gear as it folds up nice and compact and you still get that "backstop".

Rearward-retracting gear, OTOH, is totally dependent on the strength of the locking mechanism to prevent the gear collapsing on touchdown, and reinforcing that mechanism (or protecting it using additional shock-absorbing suspension in the gear struts) adds weight.

@KeithS: With the heavy engine and the light structure of that time, there was no space ahead of the center of gravity to stow away the gear. It would had needed a sliding hinge - the rearward retraction was really the only sensible option.


text:
Why is the IRST not centered on the Eurofighter Typhoon?
Following links included in this answer, I noticed the IRST is located on the left side of the Eurofighter Typhoon. It seems that this asymmetrical location is common (Dassault Rafale, MIG 29,...).
Why is the location of this device chosen so that on side seems privileged? I see no reason to prefer one side over the other, there should be the same chance for a target to be located on one side or on the other.

Have a read of the comment by moo on the top answer of the linked question. Says similar to Carlo.

The Thales UK PIRATE IRST system is located here in order to allocate space on the starboard nose for the retractable in flight refueling probe.  The port space was the only available real estate for this avionics to fit.  Other aircraft like the MiG-29 have similar restrictions in space availability.
The asymmetric location does not affect functionality; the IRST seeker head does maintain full field of view without blockage from the nose or fuselage.

Apart from space restrictions mentioned by Carlo, this is a question of forward visibility for the pilot.
On the original Su-27, the IRST was located on the centreline, but on later versions (Su-30, 35, etc.) it was offset to the right, primarily for this reason.


text:
How does auto-trim work on fly-by-wire aircraft?
As I understand, you trim to reduce the effort needed to maintain the stick in the right position. Thus, you may reach steady flight before moving the trimming wheel.
In fly-by-wire aircraft (to fix things, let's consider an A320), there is no such effort to maintain as you use sidesticks. Moreover the elevator may move almost constantly (and thus always apply some effort) to compensate turbulence (enhance stability feature).
After reading this question, I understand that trim is achieved by moving the stabilizator and that in normal law it is done by the computer (we actually see the trim wheel moving alone)
My question comes in several parts:

In flight in normal law, how and when does the computer decide it must trim the plane?
What does it take into account to trim the plane (speed? flaps configuration? average position of the elevators for the last few seconds? a mix of all? I guess average position of the elevator in a sliding time window is enough)
Does it anticipate the trim (e.g. trim before or while changing the flaps configuration)?
What happen on the ground? For example during the take off roll, I don't think there is enough data to feed an auto-trim system, but I may be mistaken.
What happen if not in normal law (I guess auto-trim would be one of the feature unavailable in alternate law)?

EDIT: althought the question may seem similar to this one, it differs as my question address the decision process used by the auto-trim system to command the flight control surface, and not the flight control surface itself (the use of stabilisator as trim in the A320)

possible duplicate of How does trim work on an A320?

@fooot the question you mention (note that my question already refers to it) address the issue of stabilisator used as trim and its answer the fact that it is handled by the ELAC (along with other useful and interesting informations). My question addresses the decision process to move the trim. Both questions are complementary and this one may go along with the other, but I think it is complex enough to be an entire question. Moreover, none of the subquestion here are addressed in the question you linked.

In fly-by-wire aircraft (to fix things, let's consider an A320), there is no such effort to maintain as you use sidesticks.

Let's be clear: there is no such effort on the pilot side, but the forces on the surfaces are still there and are taken care of by the electro-hydraulic actuators.

In flight in normal law, how and when does the computer decide it must trim the plane?
What does it take into account to trim the plane?

I will answer these two together. And let's remember what written above: the actuators are taking care of the control surfaces loads, this means that part of the actuator authority is being used to control a static load.
In an ideal situation all the authority (coming from hydraulic pressure or coil current) can be dedicated to control transients: gusts, configuration changes, turn entering, turn leaving. If you are allocating part of this authority to keep level flight, a gust (for example) that otherwise would have been easily compensated for, will lead to a momentarily loss of coordination, reducing the comfort of the passengers.
That is what (mostly) you use to trim the aircraft: if your actuator is constantly (or on average over several seconds) applying a certain force in a certain direction, the system will use the trim functionality to remove said force while not altering the flight equilibrium.

Does it anticipate the trim?

I have no public reference for this.

What happen on the ground?

Usually you leave the aircraft with no trim.

What happen if not in normal law (I guess auto-trim would be one of the feature unavailable in alternate law)?

Unless you are outside of normal law for actuator-related issues (power/hydraulic losses, for example) I see no reason why trimming would be unavailable, all that is required for trimming, as said above, is the average load on the actuators and trimming actuation capabilities.


text:
How is the length of a leg calculated?
Here are few facts:

A flight is basically climbing, staying high, then descending toward a runway

Changes in altitude increase the distance an aircraft flies. Given the climb/descent angle, this increase may be insignificant, but it still exists.

The path followed by an airliner may not be direct

Given many elements (TSA, other traffic,...) I imagine an airliner can almost never take a direct route. Not to mention the path leading to the approach.

An airport may have several runways whose length may not be the same

The departure point may be the parking position, the beginning of the runway, the end of the runway, the point where the aircraft reaches $V_2$,...
The same goes for the arriving point.

The precision of the maximum range of an aircraft is really precise

When looking at ailiners' performances, one key figure seems quite strange: the range. It seems quite precise (few miles). Lets take the ERJ-140ER as example. Its maximum range is 1250nm. Given this number, I imagine the precision is less than 10nm (3 significant digit), i.e. about 3 to 4 times an international airport's runway length (4km for dubai international airport).
Given all those elements, how is a leg length (distance of 1 flight between 2 airports) calculated for an airliner?

If you are planning to fly the maximum range to land at your destination, then you are planning to die.  Maximum range minus time to divert minus 30 minutes minus minimum "in the tanks" on landing reserve.

@Simon I thought at least the 30min reserve and the minimum in the tanks were taken into account in max range calculation. Otherwise, this is only a marketing figure with no realistic meaning.

@ManuH I don't know how Boeing and Airbus do it, but Piper and Cessna "range" figures are from full tanks to empty tanks (zero fuel).

Along the inseam.

The gap between marketing and practical application is usually large.  As voretaq says, maximum range is full to empty.  Maximum usable range is therefore something less.

You only need to plan for regulatory reserves. You don't actually have to land with them.

@rbp, you have to declare emergency if you do cut into them though and that will quite probably get you an investigation.

Many of the 'variables' you mention, are in fact fixed, and in large determined by dispatch (the smart folks at the company). For commercial flight, the flight plan will be filed in advance (generally by the company dispatch), and will contain all the waypoints en route, including expected flight levels. Dispatch makes the calculation for the most efficient flight in close collaboration with ATC authorities, for example by reserving slots on certain airways.
Deviations from the flight plan are not common - you won't hear ATC tell an airplane mid-flight to suddenly take the long way round - instead, any route alterations are communicated to the pilots when they are still on the ground, and if necessary, extra fuel is taken on board.
This flight plan is then given to the pilots, and programmed into the FMC. The FMC is a very sophisticated piece of software, and can in fact calculate the required fuel for this leg all by itself - you can even program it to calculate the best trade-off between efficiency and speed (see this KLM video at 1:40). I'm not entirely sure about the details, but you can probably program the SID and STAR of the departure and destination airports respectively as well.
On top of this, extra fuel is taken on board for things like taxi, expected holding patterns (your dispatcher will know how busy you can expect it to be at your destination airport; e.g., Heathrow is generally very busy and you might want to take some extra fuel on board), and enough fuel to at least be able to perform a few go-arounds or a diversion if circumstances call for it. In the end, the pilot is responsible for taking enough fuel on board, but will rely on the FMC and dispatch to make an educated guess.

The FMC absolutely does have the capability to navigate the SID and STAR, at least for a reasonably modern FMC. Also, changes to the planned routing happen all the time: shortcuts, vectors off course for traffic or weather, changing the arrival due to runways being closed or "turned around" as winds change, etc.  The changes aren't drastic (+/- a few miles, usually), but they are perfectly commonplace.

@RalphJ Mostly, I wasn't sure whether the STAR would be programmed on departure, since the approach might be assigned during later stages of the flight. Also, I meant to refer to substantial changes in the flight path, not minor deviations (you won't be asked by ATC to cross the Atlantic ocean on a different track 5000 feet lower)

The STAR can change, but yes, you'll put whatever arrival you were filed for in the FMC during the preflight. One benefit of this is that the arrival contains your descent profile (cross THISS at FL240, cross THATT at 250 knots & 10,000'), so your fuel predictions from the start are working from the best known Top of Descent point.

Calculating the exact amount of fuel necessary to make a trip is an inexact science, for exactly the reasons you mentioned.  The reported range is calculated for an ideal trip. Your mileage may vary.


text:
What is this door below the lavatory?
What is this door below the lavatory of this airplane?
Other aircraft have similar doors near the rear lavatory?

Called Outflow valve, used to control the cabin air pressure .


text:
Is it a standard procedure to use emergency slides without imminent danger?
On 11 Jun 2017 Easyjet U23246 from Ljubljana to London Stansted diverted to Cologne-Bonn over a "suspicious conversation". All passengers were evacuated using the emergency slides, see BBC Video.
This made me wonder why this is appropriate at all:

There was no imminent danger. It's an international airport, so surely they have at least one set of mobile stairs that could have been used in a safer manner?
Apparently nine people (of 151) needed medical attention after using the emergency slides. That's 5%!
If it had been an incident and police needed to enter the aircraft, wouldn't they arrive on mobile stairs anyway?
Apparently the airplane sat for 30min before evacuation anyway, so it wasn't even faster to use the slides.

I'm just wondering what prompted them to deploy the slides in the first place. I'm under the impression that they need to be replaced upon use and hurried evacuation didn't seem to be necessary in the first place.
As a passenger, I think a lot of people might get argumentative over not having stairs. Especially when small kids and disabled people (e.g. dependent on a wheelchair) are on-board. Not to speak of the economic and public relations impact...

You should ask is this is a standard procedure rather than ask if this was appropriate, because to assess whether it was appropriate or not, you need to get all the details, not only what was said by BBC to its public. Saying there was no imminent danger without first checking everything is fine is not possible.

@mins Well as far as I'm aware this isn't standard procedure, as similar incidents have not resulted in the use of emergency slides at airports. Also, going by your logic, imminent danger is present at every point in time, because nobody made sure 'everything is fine'. Waiting 30mins on the airfield doesn't strike me as a situation with imminent danger present though.

It is well documented that using the emergency slides would lead to injury for a small percentage of passengers (see for example the Qantas 32 documentary). This is a factor to be considered by the pilots before initiating an evacuation. However, why were the slides used and who initiated the evac in this instance, we'd have to look at official reports when they are available.

"Also, going by your logic, imminent danger is present at every point in time": That not what I meant! But everything that seemed initially suspicious must be clarified, and everything else discovered in the meantime. Maybe when the police checked the passenger past, they discovered he was traveling a lot to "potentially suspicious" locations, whatever it means. Until this is clarified, it's suspicious. Actions can be appropriate, even if spectacular. I don't know, but you don't either. That's just what I wanted to point out.

there is a rapid disembarkation using stairs, or emergency evacuation using,well, any means possible. Why was one chosen over the other, I am sure the capt has a very good and solid reason for it. Decision to evac is never taken lightly. The paperwork alone will make any captain think hard and fast...

"There was no imminent danger". The crew action revolves around this and the elements they had at that time. From this article in French: at least a backpack was blown up by police and three passengers were arrested. The airport was closed for 3 hours. It means the crew elements should have been serious enough for the possibility of a terrorism operation, and the need for preventive actions. It started with several passengers discussing about terrorism in the cabin.

Was the slide used because the cabin crew forgot to disarm the slide before opening the door maybe? That'd cause the slide to deploy, stair or no stair. Without all the data, it's impossible to come to any firm conclusions as to why whatever happened happened.

While use of the slide may have resulted in 5% injury rate, have you considered that in a panic, the injury rate of stairs is probably higher? People push and shove when spooked, and a fall from the top of the stairs could easily result in death.

If an evacuation is called for the quickest method must be used, in this case slides. No exceptions no questions. Passengers can complain after they are out but they are not given a chance to argue during the evacuation, force can be used to clear an argumentative passenger so that the other passengers can get out. The 30 minute delay was before the decision to evacuate, it has nothing to do with the actual evacuation. Full scale evacuations require no more than 90 seconds for the aircraft to be certified.
What the police need is completely irrelevant to the evacuation.
Slides can be inspected, repacked, and reused, they are test deployed at regular D maintenance inspections.(maybe C as well. D is every 6 years C is every 2 years) Emergency doors are also routinely opened for testing.
A passenger needing medical attention could very well be nothing more than a stubbed toe, light scrape, or being out of breath.

"...in this case slides. No exceptions no questions...."  Do you have a company policy or regulation you can reference for this statement? Evacuations frequently result in broken bones (i.e ankles or foot).

Emergency procedure is just that, you don't sort of evacuate or change mid emergency, the public requires simple on or off. Disemplaning(via stairs) is not evacuation, why one was chosen over the other is usually a matter of urgency but someone decided that evacuation was the appropriate action, considering disemplaning tends to take 20 minutes on a good day.
Official policy evacuation procedures are included at the beginning of every flight, on land you use the nearest exit, on water over wing exits. Somewhere in ticketing is an agreement regarding legal authority of the crews instructions.

The maximum egress time of 90 seconds is a legal requirement. http://fsims.faa.gov/WDocs/8300.10%20Airworthiness%20Insp%20Handbk/Volume%202/2_077_00.htm  CHAPTER 77.  EVALUATE FAR PART 121 EMERGENCY EVACUATION/DITCHING PROCEDURES/DEMONSTRATIONS


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Can a pilot or owner repair a seatbelt?
I have a Cessna 210 with inertia reel seatbelts.  The spring coil on the retention wheel broke.

FAR 43, Appendix A (C).14 allows for owner replacement of seat belts
FAR 43.13.(b) requires that it be restored at least to its original
or properly altered condition.
and FAR 21.9.(a).5  allows a part produced by an owner / operator to be installed

so... can I as owner / operator:

repair the spring and re-install the seatbelt
or
purchase a used seatbelt with a working coil spring (but no good webbing) and replace the coil spring?

FAR 43 is meant to allow the owner/operator to replace bolt-on components. What you are asking is the repair of the mechanism itself which may not be allowed. I think it would be worth a call to your local FSDO for an official decision.

Related https://aviation.stackexchange.com/questions/8409/how-are-owner-produced-parts-handled-under-faa-regulations?rq=1.

You cannot repair a seat belt. You can only replace it.
An owner-operator can perform preventative maintenance on their aircraft. That includes replacement of the seats and/or seat belts.

You are correct that a part may be manufactured by the owner.  However, your part will be subject of an annual inspection at which time an IA mechanic may reject the airworthiness of your part.
Your repair and installation will require your logbook entry.  As an airframe mechanic, I would review recent maintenance and be looking for a return to service tag from an approved repair station.  I would not be inclined to accept an owner-repaired reel assembly as airworthy.